Spray dryers have been used primarily for the recovery of fine powders from liquid compositions by spraying feed liquid into a heated atmospheric pressure, hot air drying chamber whereby the liquid is evaporated using hot air turbulence and the solid component is made into a powder of typically uncontrolled particle sizes. The prior art methods have the disadvantage of having particles being deposited on the inner walls of the drying chamber. The deposits prevent a switch over to other products without washing the deposits from the walls and drying the chamber which is required in a switch-over where higher purity of collected product is required.
U.S. Pat. No. 5,015,332 to Iwaya et al discloses a spray drying chamber for the separation of solids from a liquid using an ultrasonic spraying mechanism to form micro-droplets wherein the inner chamber is heated by hot air and by microwave at atmospheric pressure.